"Our most important finding is the pure existence of such an extensive icefish brooding colony," says Autun Purser of the Alfred Wegener Institute in Bremerhaven, Germany. "A few dozen nests have been observed elsewhere in the Antarctic, but this find is orders of magnitude larger."

Purser and colleagues made the discovery while surveying the Filchner ice shelf using the Ocean Floor Observation and Bathymetry System (OFOBS). "Basically this is a large, towed device, weighing one ton, which we tow behind the icebreaker RV Polarstern at a speed of one to four kilometers per hour," he explains. "We tow this at a height of about 1.5 to 2.5 meters above the seafloor, recording videos and acoustic bathymetry data."

The researchers were especially interested in this area of the seafloor because they knew it included an upwelling of water 2 degrees Celsius warmer than the surrounding bottom waters. The rest of what they found, however, was rather unexpected.

"We did not know to expect any sort of fish nest ecosystem," Purser says. That part, he adds, came as a "total surprise."

The majority of the nests they uncovered were occupied by a single adult fish guarding more than 1,700 eggs. They also observed numerous deceased fish carcasses within and near the nesting colony, suggesting that the fish play an important role in the larger food web. While more study is needed, they suspect the colony is utilized heavily by predators such as Weddell seals.